1. Field of the Invention
The present invention relates to a technology for performing a sheet folding operation by conveying a recording medium through a plurality of conveying paths.
2. Description of the Related Art
Japanese Utility Model Application Laid-open No. S62-68973 and Japanese Patent Application Laid-open No. H04-64577 disclose a sheet folding device that performs a folding operation such as an operation of folding a recording medium (hereinafter, “sheet”) in a Z fold. In such a sheet folding device, when a sheet is conveyed in a first conveying path toward a pair of folding rollers, the leading end of the sheet is brought into contact with a first stopper in the first conveying path, so that a portion of the sheet is bent by the first stopper. The bending portion is then conveyed between the folding rollers whereby a first folding operation is performed on the sheet to fold the sheet. The folded sheet is then conveyed toward a second stopper in a second conveying path, and the same process as in the first conveying path is performed in the second conveying path, so that a second folding operation is performed on the sheet to fold the sheet again. Each of the first conveying path and the second conveying path is formed by guide plates arranged on opposite sides of the sheet in a thickness direction.
However, in the sheet folding device described above, a space between the guide plates in the first conveying path is the same as that in the second conveying path, and the size of the space is not particularly specified for each of the first conveying path and the second conveying path. When the above folding operation is performed on a sheet, the sheet passing through each of the conveying paths has a different thickness, and every time the folding operation is performed on the sheet, the thickness of the sheet is increased. Specifically, the sheet passing through the first conveying path has the thickness of the original sheet because the folding operation has not been performed on the sheet yet. The sheet passing through the second conveying path has the thickness of double the original sheet because the sheet has been folded. Thus, because the thickness of the sheet is increased after the folding operation, a problem can occur if the space between the guide plates is the same in the first conveying path and the second conveying path. If the space between the guide plates is larger than the thickness of the sheet, it is difficult to convey the sheet in a stable manner or to fold the sheet at an appropriate position. On the other hand, if the space between the guide plates is smaller than the thickness of the sheet, friction between the sheet and the guide plates is increased, and therefore the sheet can be easily jammed between the guide plates.
Japanese Patent Application Laid-open No. 2002-332159 discloses a sheet folding device in which a sheet can be folded at an appropriate position in a desired manner, and can be conveyed in a conveying path without causing a jam, by setting a space between guide plates arranged downstream of folding rollers larger than that between guide plates arranged upstream of the folding rollers.
However, some sheet folding devices include a plurality of conveying paths and a plurality of pairs of folding rollers, and perform different folding operations (single fold, Z fold, outside triple fold, inside triple fold, simple quadruple fold, and gate fold) based on sheet folding modes by using different combinations of the conveying paths. In some sheet folding modes (folding operations), the thickness of a sheet conveyed through a conveying path arranged upstream of the folding rollers is the same as that in a conveying path arranged downstream of the folding rollers. In other sheet folding modes, however, the thickness of a sheet is changed (increased) when the sheet is conveyed from the conveying path arranged upstream of the folding rollers to the conveying path arranged downstream of the folding rollers. Therefore, even if the space between the guide plates arranged downstream of the folding rollers is larger than that between the guide plates arranged upstream of the folding rollers as disclosed in Japanese Patent Application Laid-open No. 2002-332159, it is difficult to convey a sheet in a smooth manner.